This invention relates to pharmaceutical containers of the type having a pierceable diaphragm to permit dispensing of a pharmaceutical from the container into a syringe.
Modern medical and pharmaceutical practices rely in part on the availability of liquid medication which is frequently presented in a pharmaceutical container. Typically, the container is provided with a pierceable diaphragm covered by a rupturable or removable seal. The diaphragm is designed to permit withdrawal of the liquid from the container by inserting a hollow needle through the diaphragm. The liquid is withdrawn through the needle and into a syringe for subsequent injection into a patient or into a pharmaceutical delivery device, such as an intravenous bag. In some applications, containers of the type having a pierceable diaphragm are multi-use containers: i.e., capable of holding more than a single dose. In such applications, the diaphragm is fabricated from a self-healing material, such as butyl rubber, so that the diaphragm can accept repeated piercing by a needle for withdrawal of appropriate aliquots.
Both unit dose and multi-dose containers are typically presented free of any pressure differential between the inner volume and ambient. As a consequence, the contents of the container are normally at ambient pressure. To withdraw liquid medication, the user initially places back pressure on a plunger of a syringe to entrain air into the syringe. Next, the seal is broken or removed, and the needle attached to the syringe is introduced into the inner volume of the container through the pierceable diaphragm. Next, air in the syringe is injected into the container by applying forward pressure on the syringe plunger, which temporarily increases the fluid pressure inside the container. Next, the plunger is withdrawn while maintaining the tip of the needle immersed in the liquid medication. The temporarily increased pressure inside the container assists in withdrawing the liquid medication easily and smoothly. When the desired amount of liquid medication has been withdrawn, the needle is removed from the diaphragm. This technique suffers from the disadvantage that the temporarily increased pressure within the container diminishes as the liquid medication is withdrawn, thereby providing reduced fluid pressure assistance for the flowing medication. In addition, if too much air is injected initially, the diaphragm can be forcibly ejected along with a portion of the medication. For those medications which are highly caustic, this can result in accidental injury to the user.
A less preferred alternative for withdrawing liquid medication from a pharmaceutical container of the pierceable diaphragm type consists of omitting the initial injection of air into the container to pressurize the inner volume and proceeding directly to the step of withdrawing the desired amount of liquid medication by applying back pressure on the syringe plunger. This technique suffers from the disadvantage of creating a pressure differential between the container interior and ambient, with the pressure inside the container lower than ambient pressure. This causes the pierceable diaphragm to be increasingly drawn inwardly of the container as the liquid medication is progressively withdrawn. For a multi-dose container, repeated forcible flexing of the diaphragm caused by creation of the pressure differential and the relaxation thereof when the needle is withdrawn can compromise the integrity of the diaphragm, particularly at those points where the diaphragm attaches to the confronting surfaces of the container. In addition, this technique suffers from the disadvantage of requiring increasingly greater traction on the plunger to remove the liquid to counteract the increasing pressure differential within the container. Further, this greater traction must be maintained until the needle is withdrawn from the diaphragm, in order to prevent the liquid from returning from the syringe into the container.
Efforts to design a pierceable diaphragm devoid of the above disadvantages have not been successful to date.